1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a fuel pump.
2. Description of Related Art
With reference to FIG. 20, a known fuel pump includes a tubular housing 11, an impeller (not shown) and a cover 22. The housing 11 has an opening 11a and receives the impeller, and the cover 22 covers the opening 11a of the housing 11. The impeller is received in a pump chamber 22a, which is formed on one axial side of the cover 22 that is opposite from the opening 11a of the housing 11. In a case of the fuel pump recited in Japanese Unexamined Patent Publication 2005-207320 (corresponding to US2005/0163605A1), a housing-side engaging portion 11y, which includes a bending portion 11b and a cylindrical portion 11c, of the housing 11 located along a peripheral edge of the opening 11a, is radially inwardly swaged, i.e., is bent against the cover 22, so that the cover 22 is fixed to the housing 11.
A clearance between the cover 22 and the impeller has a large influence on fuel flow characteristics in the fuel pump. Therefore, the manufacturing of the fuel pump is highly controlled to make this clearance to a predetermined clearance.
Specifically, the bending portion 11b of the housing-side engaging portion 11y may spring back (see an arrow SB in FIG. 20) right after the swaging. Thus, in such a case, the cover 22 may not be insufficiently urged against the housing 11. When the cover 22 is not sufficiently urged against the housing 11, an urging force (hereinafter, referred to as an axial force F1), which limits removal of the cover 22 from the housing 11, may become insufficient. In such a case, the bending portion 11b may be deformed away from the cover 22, and the cover 22 may be moved away from the impeller. Therefore, the above described clearance may be increased to deteriorate the fuel flow characteristics in the fuel pump.
In order to address the above disadvantage, the inventors of the present application have worked on a new manufacturing method by, for example, increasing a swaging load, which is applied to the housing-side engaging portion 11y of the housing 11, in view of the springing back of the bending portion 11b (see a previously proposed product A in FIG. 4). However, when an excess swaging load is applied to the housing-side engaging portion 11y and the cover 22, an undesirable deformation occurs in the bending portion 11b and the cover 22, so that the above-described clearance is significantly changed. Thus, it is not possible to control the clearance with the high degree of precision, and thereby the deterioration in the fuel flow characteristics in the fuel pump is inevitable.
Also, the inventors of the present invention have tried another method. In this method, recesses 22b (see FIG. 20) are formed on a surface of the cover 22. After the swaging of the housing-side engaging portion 11y along all around the housing 11, opposed portions of the bending portion 11b, which are axially opposed to the recesses 22b, are pressed against the recesses 22b (see a previously proposed product B shown in FIG. 4). This swaging process can substantially limit the springing back of the bending portion 11b described above, so that the sufficient axial force F1 can be exerted by the housing-side engaging portion 11y. However, the removal forcer which acts on the cover 22 to remove the cover 22 from the housing 11, is concentrated on the depressed, opposed portions of the bending portion 11b, which are opposed to and depressed against the recesses 22b. Therefore, the opposed portions are deformed away from the cover 22. As a result, the cover 22 is moved away from the impeller to increase the clearance between the cover 22 and the impeller. Thus, it is not possible to control the clearance with the high degree of precision, and thereby the deterioration in the fuel flow characteristics in the fuel pump is inevitable.